The most widely used dry-cleaning solvent is perchloroethylene, which is commonly referred to and will be referred to sometimes hereinafter as ("Perc"), which is a chlorinated hydrocarbon-based solvent. It is the dry-cleaning solvent of choice throughout North America, Europe and Asia.
In addition to Perc's use in the dry-cleaning industry, it has found extensive use as a degreasing agent in the metals industry, in scouring/milling and in various "clean room" applications in the semiconductor and electronics industry. The industrial uses of Perc are approximately tenfold greater than its use as a solvent for dry-cleaning.
While Perc has been found to be an effective dry-cleaning agent due to the fact that it does not damage synthetic fabrics or cause shrinkage to fabrics containing naturally occurring fibers, such as wool, as well as being non-flammable and possessed of a relatively low boiling point, which permits its being reclaimed and purified by means of ordinary distillation, it does present a number of other problems which present drawbacks to its use.
In particular, perchloroethylene presents a number of health and environmental hazards which would militate against its continued use, provided a substitute solvent of comparable quality were available which were free of the aforementioned hazards.
Since Perc is heavier than water, its disposal represents a significant environmental risk since it will sink to the bottom of the aquifer, lake, river, etc., with possibly resultant contamination of the water supply. Additionally, Perc vapors have been implicated as having a deterious effect on the central nervous system. In addition, due to its being a highly chlorinated molecule, Perc has been identified as being a significant health hazard to cattle, and as a cause of skin cancer, particularly melanoma, due to the action of the chlorine in Perc depleting oxygen from the ozone layer. Furthermore, and of particular import, is the fact that Perc is not biodegradable and, hence, will, over a period of time accumulate, presenting a significant industrial waste disposal hazard.
As the nature and seriousness of the foregoing problems became more and more manifest with the passage of time and with the completion of various research and clinical investigations into the nature of Perc and its mechanisms of action, the use of alternative solvents has been sought, but none have met with any degree of commercial success since they could not match the results obtained by Perc as a dry-cleaning agent.
However, at this point in time, when environmental concerns are being rigorously monitored and policed by domestic and foreign governments by means of legislation and civil and even criminal prosecution, the need for a substitute solvent for Perc for dry-cleaning operations, as well as other operations, has become a matter of some degree of urgency.
A difficulty in identifying a replacement dry-cleaning solvent for Perc is that it must meet so many requirements, both as to its efficacy as a dry-cleaning agent, i.e., non-shrinking with respect to about 160 types of fabric, dye-fast for non-bleeding with respect to about 900 types of dyes, a high flashpoint to render it non-flammable and non-combustible, the ability to separate from water, effective detergency, distillable, reclaimable, usable with existing dry-cleaning equipment, etc., as well as its being non-polluting to the water supply and the ozone layer, biodegradable, non-toxic, non-carcinogenic, etc.
One proposed solvent substitute, namely, propylene glycol monomethyl ether, which is disclosed in EP 479,146 A2 as possessing many desirable properties, was found to be wanting in that it causes damage to weak dyes and to fine yarns and to delicate fabrics, such as acetates, due to its pronounced tendency to accumulate water. Water accumulation or water-miscibility is also a decided negative from another aspect in that it significantly impairs the efficiency of the dry-cleaning process since the dry-cleaning equipment is burdened with the handling of excessive quantities of water and the solvent stock is diluted and must be brought back to a correct ratio for stability reasons.